An automobile body is usually produced such that a large number of molded panels are joined together by resistance spot welding while edge portions of panels are superimposed on each other and thus box bodies are formed, and reinforcing members or strengthening members are joined to important places of the box bodies by resistance spot welding. A member thus produced is referred to as an automobile body structural member. Examples of such an automobile body structural member include a floor cross member, a locker (a side sill), a belt line, etc. In the following description, a floor cross member is taken as an example of the automobile body structural member.
The floor cross member has a press-molded, substantially hat-like transverse cross-sectional shape composed of a top sheet, two ridgelines leading to the top sheet (hereinafter, referred to as “upper ridgelines”), two vertical walls individually leading to the two upper ridgelines, two ridgelines individually leading to the two vertical walls (hereinafter, referred to as “lower ridgelines”), and two floor flanges individually leading to the two lower ridgelines, for example. Outward flanges that are bent outwardly with respect to a cross section of the component are formed on end portions in the extending directions of the upper ridgelines and the lower ridgelines in a main body that is formed of a steel sheet and has the above transverse cross-sectional shape, the outward flanges are superimposed on a side sill inner, and then assembly is performed by resistance spot welding, arc welding, or the like. The floor cross member is an important automobile body structural member contributing to the rigidity of the car body and the suppression of the crushing of the cabin at the time of a lateral collision. Hence, until now, a large number of inventions that enhance the strength of a car body by reexamining the shapes of members and the structures of bonding portions between members and a large number of inventions regarding methods for producing members have been disclosed.
Patent Literature 1 discloses an invention in which the performance of a member is enhanced by continuously forming a top sheet, vertical walls, and outward flanges adjacent to upper ridgelines that are provided in an end portion in the longitudinal direction of a press-molded product having a hat-like cross section. Patent Literature 2 discloses an invention in which the bonding strength between a side sill and a floor cross member is enhanced by providing an opening in a side surface of a side sill inner and welding together a sill inner reinforce and the floor cross member placed in the interior of the side sill. Patent Literature 3 discloses an invention in which the bonding strength between a side sill and a floor cross member is enhanced by opening a side sill inner without enlarging the transverse cross section and providing a plurality of welds for bonding with the floor cross member.